A demand exists for retroreflective materials having printed patterns or graphics formed thereon. Retroreflective material is capable of reflecting the predominant portion of light rays impinging thereon in a substantially parallel path toward the source of the light. A particularly efficient type of retroreflective element employs molded members of cube-corner formations. Cube-corner reflectors molded from glass and more recently from acrylic resins or oligomers have commonly been employed as safety devices on bicycles, automobiles and other vehicles.
Rowland in U.S. Pat. No. 3,689,346, incorporated herein in its entirety by reference, describes a process in which retroreflective sheeting is produced on a continuous basis by applying transparent sheet material over a hardenable molding material previously deposited upon a moving mold surface, after which the molding material is solidified and bonded to the sheet material to produce a composite structure. The mold surface has an array of minute, contiguous cube-corner recesses therein, so that the sheeting correspondingly has a multiplicity of closely spaced cube-corner formations spaced about and projecting from a smooth surface of the sheet material, which provides the body portion thereof.
Bernard et al., U.S. Pat. No. 5,643,400, also incorporated herein in its entirety by reference, describes a continuous process for making lengthy sheets of "seamless" retroreflective sheeting using mold surfaces formed on a pair of rotatable drums.
Brown, U.S. Pat. No. 4,082,426 discloses a method of introducing markings into retroreflective sheeting which are visible when the sheeting is viewed at an angle under retroreflective viewing conditions to enable a viewer to determine the identity of the sheeting. The markings are provided on a transparent image layer disposed between a spacing layer and a specularly reflective layer. Palmquist in U.S. Pat. No. 2,354,049 discloses a stop sign having embossed (raised) lettering upon which a separate sheet of reflex light-reflector (retroreflector) material is applied to provide improved sight visibility. The beaded or retroreflective areas of the sheet are covered with black ink or paint in the raised letter areas to make the letters stand out more plainly.
Reininger in U.S. Pat. No. 2,231,139 discloses a sign structure in which the sign character is formed of protuberances formed integral with a translucent plate to produce reflection of incident light.
Phillipppi in U.S. Pat. No. 2,422,256 discloses a decalcomania transfer of retroreflective elements in which the sign design is pasted upon a decal base and coated with reflex-reflecting elements.
Coburn et al. in U.S. Pat. No. 4,656,072 produced colored indicia in retroreflective articles by patterns produced using colored adhesives which are visible behind retroreflective material.
Bradshaw et al. in U.S. Pat. No. 4,952,023 discloses an internally illuminated sign in which a graphic on a transparent face sign is made visible from the front of the sign by retroreflected light, internal illumination or both.
Despite the many efforts by those skilled in the art, and the above represents only a small sampling, there still remains an unfulfilled need for a high speed, high quality, low cost process of producing printed patterns for graphic, decorative and other utilitarian purposes on retroreflective sheeting.